HEMOGLOBIN OXYGEN-AFFINITY IS INCREASED IN ERYTHROPOIETIC PROTOPORPHYRIA

Whole blood and hemolysates from seven normal and three erythropoietic protoporphyria patients were compared in terms of their hemoglobin fu nction. The oxygen affinity (P50) of the erythropoietic protoporphyria hemolysates compared to normals (13.1 +/- 0.2 vs 17.5 +/- 0.3 mmHg; P < 0.00 1) and erythropoietic protoporphyria erythrocytes compared to normals (23.4 +/- 0.6 vs 27.1 +/- 0.5 mmHg; P < 0.00 1) were increased while oxygen-binding cooperativity (n-value of the H-11 equation) wer e similar. We conclude that hemoglobin function in erythropoietic prot oporphyria patients is altered, but without pathophysiologic consequen ces. Because hemoglobin in which protoporphyrin IX substitutes for hem e has a low oxygen affinity, our findings of a higher than normal affi nity in erythropoietic protoporphyria red cells and hemolysates may in directly support the findings by others that protoporphyrin IX binds t o hemoglobin at non-heme-binding sites. In addition, based on the effe ct of other abnormal hemoglobins, this shift in P50 will decrease any tendency for anemia in erythropoietic protoporphyria patients.